Encryption is applied only to the content of files. It is performed after compression, and not to any other associated data. The file data is encrypted byte-for-byte...

To remove encryption from the files that have been zipped, they would need to be extracted using the correct password. WinZip uses the password in combination with the appropriate key to decrypt the zipped data and recreate exact byte-for-byte duplicates of the originals. Once the files have been extracted, you can create a new Zip file without applying encryption. Afterwards, you can delete the encrypted Zip file, leaving only the new, unencrypted Zip file.